WASHINGTON — Representative Katherine M. Clark looks around the US Capitol and sees nothing but possibility.

Never mind that Congress is hopelessly gridlocked on most major issues and only recently began pulling back from the constant threat of fiscal crisis. On her third day in her new Washington office, the Massachusetts Democrat, elected to fill the unfinished House term of Senator Edward J. Markey, insisted she could deliver on her promises to improve economic opportunities and women’s rights that she made during the campaign.

Sure, the House is run by her ideological opposites, Republicans who loathe spending on social programs she favors almost as much as they loathe President Obama. And of course she is near the lowest rung in seniority.

But, she insists, “as you get to know people and you get to talk to them on a one-on-one basis, you realize that it really is the same motivations.”

She added: “There certainly seem to be those here who play an obstructionist role, and those aren’t going to be the members that I’m going to be able to partner with and work with.”

And how long will she maintain such a rosy outlook, given the discouraged tone of most of her fellow Democrats who serve in the minority in the GOP-run House?

“It is not my nature to be cynical, so I’m certainly not going to set a date for turning into one,” she said, maintaining a fixed gaze and a steady smile.

Victorious in a Dec. 10 special election and sworn in just as Congress was heading off for its holiday vacation, Clark returns this week to a Congress that has set new records for futility. Even senior lawmakers like Markey, who held the seat for nearly 37 years before his election to the Senate, complain of a paralysis that has made even routine accomplishments insurmountable.

But the 50-year-old Clark, like almost everyone
else in Congress, was elected on a sunnier platform, with promises to break through the dysfunction. The former state senator emerged from a crowded Democratic primary with a relentlessly disciplined message: She would fight for equal pay for women, preserve social service programs, and promote the economic interests of the district. The priority list was fine-tuned to appeal to the core Democratic voters in her district.

In an hourlong interview Wednesday morning, she said she would keep trying win broader support for those issues. She smiled and laughed, occasionally clutching at a necklace of large pearls, as she returned repeatedly to the type of hopeful language she used on the campaign.

“That also doesn’t mean that I am not looking at this clear-eyed and that I don’t see the difficulties that are going to be ahead of us, and that this is a Congress that has had a record-low session as far as passing bills and productivity,” she said. “So we have very real challenges, and I take them seriously, and I see them objectively.”

Clark remains in the orientation phase. Wednesday, she shook hands and nodded as House minority leader Nancy Pelosi took her aside and introduced her to Representative George Miller, one of Congress’s most senior Democrats, who once chaired the natural resources committee, the same committee Clark was appointed to serve on Wednesday. And like an excited tourist, she pulled out her blue iPhone to snap a picture of Pelosi’s new San Francisco 49ers bracelet.

“That’s great,” Clark said, as Pelosi took her to a special ceremonial office once used by House Speaker Thomas P. “Tip” O’Neill Jr. Clark noted that she was friendly with O’Neill’s son, Thomas P. O’Neill III, the former Massachusetts lieutenant governor who now runs a public relations and lobbying firm.

This is “our special little Massachusetts area,” Pelosi said, showing Clark a glass gavel she received from the former speaker’s family, and a picture of a teenaged Pelosi with President John F. Kennedy.

Pete Marovich for the Boston Globe

“We have very real challenges,” said clark, “and I take them seriously, and I see them objectively.”

It was a time capsule, a stark contrast to the modern era, when the state delegation’s clout is significantly diminished. But even Kennedy was once a freshman congressman.

Clark said it has been “surreal” to occupy Markey’s former office suite, a vast space with one of the best views of the Capitol dome. Her colleague, Somerville Democrat Michael E. Capuano, told her to enjoy the choice office real estate while she can because she will surrender it to a more senior lawmaker if she is reelected in November. Clark is still waiting to hear if she will draw an opponent for this year’s election in her heavily Democratic district, which covers all or part of 24 municipalities stretching from Revere to Woburn to Holliston.

When Markey occupied the office, political memorabilia and framed copies of landmark legislation dating to the 1970s covered the walls. Now they are barren, and only a few of the cubicles are filled with staff members.

“This is my third day,” Clark said several times, trying to explain her struggles on a variety of matters, including her inability to remember the names of the lawmakers she has met or her uncertainty over which issues might separate her from other Democrats.

Clark said she has rented a small apartment near Nationals Park, the baseball stadium in Southeast Washington, where she will stay when Congress meets. Clark’s husband and three sons will remain in Melrose.

She remained cautious when questioned on a key issue, declining to say whether she would support increased sanctions against Iran. Clark said she would like to give negotiations a chance, that Israel’s interests must be considered, and that Iran must not obtain nuclear weapons.

She sticks with the state’s liberal delegation on most issues, including opposition to Obama’s willingness to consider reducing the annual cost of living adjustment for Social Security recipients.

Clark said she hopes to find some bipartisan priorities, including energy conservation and heating assistance for low-income residents, to bridge the gap with Republicans. She said she was surprised during her swearing-in ceremony when she was greeted effusively by Representative Joe Wilson, a South Carolina Republican, who was thrilled to learn that she had a son named Addison, Wilson’s given name. That’s the same Joe Wilson who is best known for shouting “You lie” during Obama’s speech to a joint session of Congress in 2009.

“I actually put it together later,” Clark said, laughing as she recalled how she connected Wilson to his headline-grabbing moment.

“He was extremely friendly and I think long ago chose to go by Joe, not Addison,” she said. “But he was excited to meet my son named Addison.”

Globe correspondent Kimberly Railey contributed to this article. Noah Bierman can be reached at nbierman@globe.com. Follow him on Twitter @noahbierman.